Multi-layer inductor

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-43556, filed on 17 Mar. 2021, the entire contents of which are incorporated herein by reference.

The present disclosure relates to a multi-layer inductor.

Known in the art is an inductor including a through conductor linearly extending in an element body has been known. Japanese Patent Application Laid-Open No. 2020-88289 discloses an inductor including an element body having a pair of end surfaces facing each other, a through conductor extending flatly between the end surfaces, and a pair of external electrodes provided on both the end surfaces of the element body and connected to the through conductor.

The above-described element body of the inductor according to the conventional art is a sintered body (sintered element body) obtained by sintering a plurality of magnetic material layers stacked. The through conductor is obtained by sintering the conductive paste applied on the magnetic material layer together with the magnetic material layer. In general, the shrinkage rate of the magnetic material layer and the shrinkage rate of the conductive paste at the time of sintering are different. Therefore, an internal stress due to a difference in shrinkage rate is generated in the element body after sintering, and cracks caused by the internal stress may be generated in the element body. As a result of intensive studies, the present inventors have newly found a technique capable of preventing cracks caused by internal stress.

According to an aspect of the present disclosure, a multi-layer inductor in which cracks are prevented is provided.

A multi-layer inductor includes, a sintered element body including a plurality of layers stacked and having a pair of end surfaces facing each other in a first direction orthogonal to a stacking direction of the plurality of layers, a through conductor provided in the sintered element body and extending between the pair of end surfaces, both end portions of the through conductor are exposed at the end surfaces, and a pair of external electrodes provided on the end surfaces of the sintered element body and covering both the end portions of the through conductor exposed to the end surfaces, respectively, wherein the through conductor includes, a pair of extracting conductors respectively constituting both the end portions of the through conductor and each having a first end portion exposed from the end surface of the element body and a second end portion located inside the element body, and an inner conductor connecting the pair of extracting conductors to each other and having ends overlapping the second end portions of the extracting conductors in the stacking direction of the plurality of layers.

In the above multi-layer inductor, the through conductor includes the extracting conductor and the internal conductor, and the second end portion of the extracting conductor and the end portion of the internal conductor overlap each other in the stacking direction of the element body. The amount of shrinkage of each of the extracting conductor and the internal conductor during sintering is small, and internal stress generated in the element body after sintering can be prevented. Therefore, in the above multi-layer inductor, cracks caused by internal stress can be prevented.

In the multi-layer inductor according to another aspect, the extracting conductor is shorter in the first direction than the inner conductor in the first direction.

The multi-layer inductor according to another aspect further includes a step portion formed by the second end portion of the extracting conductor and the end portion of the inner conductor overlapping the second end portion.

In the multi-layer inductor according to another aspect, the through conductor comprises a plurality of the inner conductors, each of the inner conductors extends parallel to the first direction, and the ends of the internal conductors adjacent to each other in the first direction overlap each other in the stacking direction of the plurality of layers.

Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant description will be omitted.

The configuration of a multi-layer inductor according to an embodiment will be described with reference to. As shown in, the multi-layer inductoraccording to the embodiment includes an element bodyand a pair of external electrodesA andB.

The element bodyhas a substantially rectangular parallelepiped outer shape and includes a pair of end surfacesandfacing each other in the extending direction of the element body. The element bodyfurther includes four side surfacestoextending in the facing direction of the end surfaceandto connect the end surfacesandto each other. The side surfaceis a mounting surface facing the mounting substrate when the multi-layer inductoris mounted, and the side surfacefacing the side surfaceis a top surface when the multi-layer inductoris mounted. The dimensions of the element bodyare, for example, 2.5 mm length×2 mm width×0.9 mm thickness, where a dimension in the facing direction of the end facesandis a length, a dimension in the facing direction of the side facesandis a width, and a dimension in the facing direction of the side facesandis a thickness.

The element bodyhas a configuration in which a through conductoris provided inside a magnetic body. As shown in, the element bodyhas a stacking structure in which a plurality of magnetic material layersconstituting the magnetic materialare stacked in the facing direction of the side surfacesand. In the following description, the facing direction of the side surfacesandis also referred to as a stacking direction of the element body, and the facing direction of the end surfacesandorthogonal to the stacking direction of the element bodyis also referred to as a first direction.

The magnetic bodyis made of a magnetic material such as ferrite. The magnetic bodyis obtained by stacking a plurality of unsintered magnetic bodies (green sheets or green paste layers) to be the magnetic material layerand sintering. The number of magnetic material layersconstituting the element bodyis, for example, 150. In the actual element body, the plurality of magnetic material layersare integrated to such an extent that the boundaries between the layers cannot be visually recognized.

As shown in, the through conductorextends between the pair of end surfacesand. The through conductorincludes a plurality of conductors, and formed of a pair of extracting conductorsandand a pair of internal conductorsandin the present embodiment. The through conductoris made of a metal material. In the present embodiment, the through conductoris made of Ag.

The pair of extracting conductorsandconstitute both ends of the through conductor, respectively. More specifically, the extracting conductorconstitutes an end portion of the through conductorlocated on the end surfaceside, and the extracting conductorconstitutes an end portion of the through conductorlocated on the end surfaceside. Each of the pair of extracting conductorsandhas a substantially rectangular flat plate shape and extends parallel to the side surface. As shown in, the pair of extracting conductorsandare located between different layers of the plurality of magnetic material layers. More specifically, the extracting conductoris located farther away from the side surfacethan the extracting conductor.

The extracting conductorhas a first end portionand a second end portionas end portions in the facing direction (first direction) of the end surfacesand. The first end portionis exposed from the end surface. The second end portionis located inside the element body. The extracting conductorhas a slip shape extending along the first direction, and the first end portionis relatively wide. The extracting conductorhas a first end portionand a second end portionas end portions in the first direction. The first end portionis exposed from the end surface. The second end portionis located inside the element body. The extracting conductorhas a slip shape extending along the first direction, and the first end portionis relatively wide.

The pair of extracting conductorsandhave lengths Land Lin the first direction, respectively. The lengths Land Lare both shorter than the length L of the element bodyin the first direction. The length Lof the extracting conductorsand the length Lof the extracting conductorsmay be equal to or different from each other.

The pair of internal conductorsandcooperate to connect the pair of extracting conductorsand. More specifically, the pair of internal conductorsandare arranged in the order of the internal conductorand the internal conductorfrom the extracting conductortoward the extracting conductor. Each of the pair of internal conductorsandhas a rectangular flat plate shape and extends in parallel to the side surface. As shown in, the pair of internal conductorsandare located between different layers of the plurality of magnetic material layers. More specifically, the inner conductoris located farther from the side surfacethan the inner conductor.

The internal conductorhas a first end portionat the end surfaceside and a second end portionat the end surfaceside as end portions in the first direction. Similarly, the internal conductorhas a first end portionat the end surfaceside and a second end portionat the end surfaceside as end portions in the first direction.

The pair of internal conductorsandhave lengths Land Lin the first direction, respectively. The lengths Land Lare both shorter than the length L of the element bodyin the first direction. The length Lof the inner conductorsand the length Lof the inner conductorsmay be equal to or different from each other. The lengths Land Lof the inner conductorsandmay be designed to be longer than the lengths Land Lof the extracting conductorsand.

As shown in, the first end portionof the internal conductorand the second end portionof the extracting conductoroverlap each other in the stacking direction of the element body. More specifically, the first end portionof the inner conductoroverlaps the end portionof the extracting conductorfrom the upper side (that is, the side surfaceside). As a result, the extracting conductorand the internal conductorare joined and electrically connected to each other. Further, a step portionis formed at a joint portion between the first end portionof the inner conductorand the second end portionof the extracting conductor.

The second end portionof the inner conductorand the second end portionof the extracting conductoroverlap each other in the stacking direction of the element body. More specifically, the second end portionof the internal conductoroverlaps the end portionof the extracting conductorfrom the lower side (that is, the side surfaceside). As a result, the extracting conductorand the internal conductorare joined and electrically connected to each other. Further, a step portionis formed at a joint portion between the second end portionof the inner conductorand the second end portionof the extracting conductor.

Further, the second end portionof the internal conductorand the first end portionof the internal conductoroverlap each other in the stacking direction of the element body. More specifically, the second endof the internal conductoroverlaps the endof the internal conductorfrom the lower side (that is, the side surfaceside). As a result, the pair of internal conductorsandare joined and electrically connected to each other. A step portionis formed at a joint between the second end portionof the inner conductorand the first end portionof the inner conductor.

In this manner, the through conductorhas three step portionsto, and the four conductorstoconstituting the through conductorare disposed in a step manner. The four conductorstoare gradually apart from the side surfacefrom the extracting conductortoward the extracting conductor.

The pair of external electrodesA andB are provided on the end surfacesandof the element body, respectively. The external electrodeA covers the entire region of the end surface, and is joined in direct contact with the end portion of the through conductorexposed at the end surface. Similarly, the external electrodeB covers the entire region of the end surfaceand is joined in direct contact with the end portion of the through conductorexposed to the end surface. In the present embodiment, as shown in, the external electrodesA andB integrally cover the end surfacesandand the side surfacestoof the region adjacent to the end surfacesand. Each of the external electrodesA andB is formed of one or more electrode layers. A metallic material such as Ag, for example, can be adopted as an electrode material constituting each of the external electrodesA andB.

Subsequently, a method for forming the element bodyincluding the through conductordescribed above will be described with reference to.

In forming the through conductor, firstly, a green sheetto be a part of the element bodyis prepared as shown in. The green sheetmay be formed of a single layer or a plurality of layers. Then, as shown in, the extracting conductoris provided at the edge of the green sheetserving as the end surfaceof the element body. At this time, the extracting conductoris in a conductive paste state and has not yet been sintered. The conductive paste is applied by, for example, screen printing. Next, as shown in, a green paste layeris applied and formed on the entire rectangular region from the extracting conductorto the edge of the green sheetserving as the end surfaceof the element bodyon the green sheet

Subsequently, as shown in, the internal conductorin a conductive paste state is provided on the green paste layerand the second end portionof the extracting conductor. The inner conductoris provided such that the first end portionoverlaps the second end portionof the extracting conductor. Next, as shown in, a green paste layeris applied and formed on the green paste layer. More specifically, the green paste layeris provided entirely in a rectangular region from the internal conductorto the edge of the green sheetserving as the end surfaceof the element body. Further, a green paste layercovering the entire extracting conductoris also applied and formed. Further, as shown in, the internal conductorin a conductive paste state is provided on the green paste layerand the second end portionof the internal conductor. The inner conductoris provided so that the first end portionoverlaps the second end portionof the inner conductor.

Subsequently, as shown in, a green paste layeris applied and formed on the green paste layer. More specifically, the green paste layeris entirely provided in a rectangular region from the internal conductorto the edge of the green sheetserving as the end surfaceof the element body. A green paste layerintegrally covering the extracting conductorand the internal conductoris also applied and formed. Next, as shown in, the extracting conductorin a conductive paste state is provided on the green paste layerand the second end portionof the internal conductor. The extracting conductoris provided so that the second end portionoverlaps the second end portionof the internal conductor. Further, as shown in, a green paste layerintegrally covering the extracting conductorand the pair of internal conductorsandis applied and formed. Then, a green paste layer (not shown) integrally covering the pair of extracting conductorsandand the pair of internal conductorsandis applied and formed to obtain an unsintered body.

Thereafter, the green bodyis subjected to a sintering treatment to obtain the above-described element body. Finally, the external electrodesA andB are provided on the end surfacesandof the element body, respectively, to complete the multi-layer inductordescribed above.

As described above, in the multi-layer inductor, the through conductorprovided in the sintered element bodyincludes the pair of extracting conductorsandand the pair of internal conductorsand, and the second end portionsandof the extracting conductorsandand the end portionsandof the internal conductorsandoverlap each other in the stacking direction of the element body.

The adjacent conductorstoare electrically connected to each other at their ends, and function as the through conductoras a whole. In addition, in the facing direction of the end surfacesand, the lengths Lto Lof the conductorstoare shorter than the lengths L in a case where the through conductor is formed of one flat conductor. Thus, the amount of shrinkage of each of the conductorstoduring sintering of the element bodyis reduced, and internal stress generated in the element bodyafter sintering is prevented. Therefore, in the multi-layer inductor, cracks caused by internal stress are prevented.

In the multi-layer inductor, the lengths Land Lof the pair of extracting conductorsandare designed to be shorter than the lengths Land Lof the internal conductorsand. In this case, the amount of shrinkage of the extracting conductorsandduring sintering of the element bodyis reduced. Therefore, for example, a situation in which the extracting conductorsandenter the inside of the element bodyfrom the end surfacesandis prevented, and a connection failure between the extracting conductorsandand the external electrodesA andB is effectively prevented.

Although the embodiments of the present disclosure have been described above, the present disclosure is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present disclosure. For example, the number of internal conductors of the through conductor is not limited to two, and may be one or three or more. The pair of extracting conductors may be located between the same layers of the plurality of layers.